MEMS (microelectromechanical systems) or micromachines are devices in which micromachine elements, electronic circuits, and optical devices are integrated, and are studied for many applications and used practically (see Non Patent Literature 1). Since these devices, though being small-size components based on semiconductor production technologies, execute complicate and advanced functions, the devices are used as important components holding the key to microsystems including various types of sensors, printer heads, disk heads, optical switches for communication, and biochips. Devices in these fields, unlike usual semiconductor production, necessitate resists capable of being patterned in a high aspect ratio (which means “a height of a structure/a width thereof”).
A production method of structures having a high aspect ratio often employs a pattern formation process using X-ray lithography of a photosensitive resin composition, referred to as a “LIGA process” (see Non Patent Literature 2). However, the LIGA process has drawbacks including necessitating a high-priced X-ray apparatus and necessitating long-time X-ray irradiation. Due to demands including resource saving, energy saving, workability improvement, and productivity improvement, applications of inexpensive high-productivity UV (ultraviolet rays) lithographic systems are paid attention to.
However, positive resists based on the dinaphthoquinone-novalac reaction in UV lithographic systems are not suitable for applications requiring a film thickness of 50 μm or more. That film thickening has such a limitation is because dinaphthoquinone-type (DNQ) photoreaction products exhibit relatively high light absorption at near-ultraviolet wavelengths (350 to 450 nm) generally used for resist exposure. Sidewalls peculiar to DNQ-type photoresists assume not a straight shape but rather a slope shape due to the difference in solubility between the exposure region and the non-exposure region in a developing liquid. Furthermore, the irradiation intensity at the bottom portion of a resist is known to be lower than that at the surface because the resist itself absorbs irradiated light, and in the case where the light absorption capability of a resist itself is extremely high, underexposure of the bottom portion becomes remarkable, and the sidewalls assume a slope shape or a distorted shape.
Patent Literature 1 describes that a negative chemically-amplified thick-film resist composition composed of a propylene carbonate solution of a polyfunctional bisphenol A novolac epoxy resin, a photoacid generating agent, and an aromatic sulfonium hexafluoroantimonate exhibits a very low light absorption in the wavelength region of 350 to 450 nm. The resist composition is applied on various types of substrates by spin coating, curtain coating, or the like, thereafter baked to volatilize the solvent to thereby form a solid photoresist layer having a thickness of 100 μm or more, and further irradiated with near-ultraviolet light through a photomask by using one of various types of exposure methods such as contact exposure, proximity exposure, and projection exposure to be thereby subjected to a photolithographic processing. Then, the resultant is immersed in a developing liquid to thereby dissolve the non-exposure region, whereby high-resolution negative images of the photomask can be formed on the substrates. The Patent Literature also discloses similar means for such an application as a dry film resist coated on a base material such as a polyester film. However, the development of the composition uses an organic solvent. Because organic solvents can affect the environment and for other reasons, resists forming high-aspect ratio structures capable of being developed with an alkali have been demanded. Patent Literatures 2, 3 and 4 each disclose resist compositions capable of being developed with an alkali aqueous solution as chemically amplified thick-film resists. However, because the compositions cause coloration by heat and yellowing with time, the compositions cannot be used in the fields requiring transparency.
On the other hand, Patent Literature 5 discloses a resin composition for optical three-dimensional shaping containing a specific epoxy compound as a resin composition excellent in transparency. However, because the resin composition cannot be developed with an alkali aqueous solution, fine patterns cannot be formed by photolithography using existing lines for semiconductors, LCDs, MEMSs, and the like.
In recent years, in fields requiring transparency, including displays such as LCDs, partition walls for electronic papers and organic ELs, and the like, resists providing structures capable of being developed with an alkali and having a high aspect ratio and transparency have been demanded, but no resists satisfying all the properties have been found.